In the LTE and LTE-A standards, a TDD system frame is composed of ten subframes. The 3GPP supports totally seven types of frame structures, as shown in Table one.
TABLE ONETDD system uplink and downlink frame structureUplinkHandoverandpointdownlink periodstructurefromsequencedownlinkSubframe numbernumberto uplink01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD6 5 msDSUUUDSUUD
Currently in the 3GPP standard, the UE is notified of a frame structure configured by a current serving cell through system information SIB-I. According to the existing standard, a minimum change period of the SIB information is 640 ms. In a pre-research project of “dynamic TDD frame structure” formally approved by the 3GPP in the RAN54 (December 2011) plenary session, it is possible to more dynamically allocate the TDD system frame structure. The change period of the TDD system frame structure is shortened to make full use of the TDD characteristics so as to better support asymmetric traffic transmission.
However, there is no specific solution about how to set the retransmission of a downlink data frame. Further, in the uplink synchronous HARQ process, a further solution about how to retransmit PUSCH to avoid conflict with the R10UE is also needed.